[Fedora] cups.service.in: Use 'notify' service type and run after network.target

[Fedora] cups.service.in: Use 'notify' service type and run after network.target

1) If the service is defined with 'simple' type, the result of 'systemctl' is 0 regardless of actual startup result, because it reports success/failure of forking process (even before cupsd is started). This way errors due bad configuration or programming errors are masked during systemctl invocation.
The 'notify' type depends on executable sending a 'Im running' type of message to systemd after successful start and systemctl's return code depends whether this message came or not, which solves the issue.
2) The service needs to be started after all units needed for network.target are activated. This prevents starting cupsd before we have ports ready.

Fedora bugs:
https://bugzilla.redhat.com/show_bug.cgi?id=1153660 (adding network.target)
https://bugzilla.redhat.com/show_bug.cgi?id=1088918 (change of the service type)